This chapter focuses on technology for construction of recombinant adenoviruses containing reporter genes under the control of putative regulatory regions of the human (h)CYP19 (aromatase) gene, as well as expression vectors. These recombinant adenoviruses have been used in primary cultures of human placental cells to characterize regulatory regions of the hCYP19 gene and to analyze the function of transcription factors on hCYP19 expression and on trophoblast differentiation.